This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2001-265553 filed on Sep. 3, 2001 and 2002-164012 filed on Jun. 5, 2002.
The present invention relates to a fuel injection pump having a throttled fuel path for fuel lubrication, which is used for an internal-combustion engine (engine).
In a cylinder injection type engine in which fuel is injected directly into a cylinder, injection pressure of fuel must be very high for atomizing the injection fuel. Accordingly, the fuel is drawn from a fuel tank by a low-pressure fuel pump such as a feed pump serving as a preliminary pressure source and, then, it is fed under high pressure to a fuel injection valve by a plunger pump.
Generally, the fuel injection pump has a drive shaft driven through a gear or a belt by a crankshaft of the engine. The drive shaft, which is driven by the engine, activates the plunger pump and the feed pump of the fuel injection pump. In this way, pressurization of the fuel is easily achieved by using driving force of the engine.
The feed pump, which is an inner gear type trochoid pump, draws the fuel from the fuel tank and discharges it to a fuel pressurizing chamber for the plunger pump in such a manner that each volume of teeth gaps between inner and outer gears in mesh varies in a trochoid curve. Here, feed pressure equivalent to discharge pressure from the feed pump is stabilized within a predetermined range by a pressure control valve.
The fuel injection pump is provided between the feed pump and a pump-cam chamber which contains the drive shaft and a cam rotating along with the drive shaft with a bypass conduit for fuel lubrication, so that a part of the fuel from the feed pump is fed for lubricating the pump-cam chamber. In the fuel injection pump mentioned above, discharge pressure of the feed pump driven by the engine is responsive to engine revolution, and an amount of the fuel fed from the feed pump to the pump-cam chamber is sufficiently large, when the engine revolution is high, so that engine performance is reliable. However, the feed pressure of the feed pump is relatively low when the engine revolution is low. Even though the fuel discharged from the feed pump to the fuel pressurizing chamber for the plunger pump is relatively small, the fuel is also fed partly for lubricating the pump-cam chamber. Accordingly, the feed pressure is too low to adequately feed the fuel to the fuel pressurizing chamber, which causes a problem of poor engine performance, in particular, when the engine starts up.
To cope with this problem, it is conceivable that the bypass conduit from the feed pump to the pump-cam chamber is provided with a throttle for controlling the feed of lubrication fuel to the pump-cam chamber. However, in a conventional aperture-type throttle as shown in FIG. 11, a foreign material mixed in the fuel is likely to be trapped by the throttle, so that the bypass conduit may be thoroughly blocked off. As the result, the fuel is not sufficiently fed for lubricating and cooling the drive shaft and the cam in the pump-cam chamber, which results in poor reliability due to the possible burn-in of the drive shaft and the cam.
An object of the present invention is to provide a fuel injection pump in which a fuel path for fuel lubrication is unlikely to be blocked off by a foreign material mixed in the fuel. Another object thereof is to provide a fuel injection pump having a throttled fuel path whose construction is simpler. A further object thereof is to provide a fuel injection pump whose drive shaft and cam are well lubricated without burn-in thereof.
To achieve the above objects, a throttle member is disposed in a fuel path from a preliminary pressure feed source to a pump-cam chamber. The throttle member is composed of a first gap formed between an inside wall and a movable member and a second gap between the movable member and a seat, when the movable member is in contact with the seat. Thereby, even if the foreign material mixed in the fuel is trapped on the first or second gap, only a part of the first or second gap is blocked off and necessary fuel flow can be secured. In addition, the throttle member controls an amount of the fuel with the first gap.
Further, when the fuel flow stops and the movable member leaves the seat, the blockage of the foreign material is completely released. It is preferable that the movable member is a sphere, freely movable within the inside wall and the inside wall is formed in shape of a cylinder. The seat may be formed in shape of a part of a circle or semi-circle. The seat may be provided with cuts through which the fuel flows from an upstream side thereof to a downstream side thereof and which constitutes the second gap.
According to the present invention, the fuel injection pump is highly reliable, in particular, at a high engine revolution range, resulting in the prevention of burn-in of the drive shaft and the cam in the pump-cam chamber.